The essential characteristics of the new Synchronous Digital Hierarchy (SDH) are set forth in CCITT-Recommendations G.707, G.708 and G.709. As with asynchronous hierarchies, the new synchronous hierarchy also contains multiplex signals with different bit rate frequencies. However, the multiplex signals of the synchronous digital hierarchy have other bit rate frequencies, and a different frame structure as well.
The elemental multiplex signal of the synchronous digital hierarchy is characterized as an STM-1 signal (synchronous transport module) and has a bit rate frequency of 155 kbit/s. Other multiplex signals can be formed by byte interleaving several STM-1 signals. These multiplex signals are called STM-N signals, where N indicates the number of STM-1 signals. The frame structure of the multiplex elements is byte oriented. One byte consists of eight bits. The frame of the STM-1 signal consists of nine lines and 270 columns for each one byte. The transmission sequence is by bytes and lines from top to bottom. The first nine columns contain the Section Overhead (SOH)--hereafter called head part. The remaining columns of the STM-1 signal contain the Payload--hereafter called functional part. No further details are provided, since the functional part's structure is not essential to understand the invention.
The head part contains signals assigned to a transmission line, such as the frame identification word, which consists of 6 bytes, the synchronization bytes A1, A2, byte B1, which serves to monitor a regeneration section, byte F1, which is transmitted by the service channel, or bytes for national use. To monitor a regeneration section, the CCITT-Recommendations G.783 and G.958 require measuring the transmission error probability, and to form the parity of the bits from an entire frame, and then transmit these in the following frame with the parity word B1. The parity word B1 is then checked and newly formed by each intermediate generator.
A well known process, the Bit Interleaved Parity (BIP) process, is used to determine the transmission error probability. It produces an N-bit code, where N is a whole number (integer), which is eight in the parity word B1.
This requires an intermediate generator, which complies with CCITT-Recommendation G.783 and G.958, needing an extensive circuit to determine the parity, and a device to evaluate and describe the parity word B1, in addition to a synchronization circuit, and other signal processing installations, such as a demultiplexer and a multiplexer.
The invention now has the task of creating a process and a device to realize it, making it possible, with simple means, to determine the transmission error probability during the transmission of SDH signals.